Stream test logs to custom test runner

Hello,

I'm looking into writing a custom test runner for the purpose of better integrating with CI. The two features that I care most about right now are segregating test outputs and retriggering of specific tests.

I was wondering what the recommended way of streaming test outputs was. It seems like `orchestrator_client.execute2` only provides execution responses once the test is done, which does not let users follow ongoing test executions.

It seems like a custom `TestExecutor` doesn't have those capabilities. I've also started to look into writing a custom orchestrator, but that looks like a significantly bigger endeavor.